This invention relates to an apparatus for the variable-speed control of an escalator.
Conventional control apparatus for escalators have employed a system wherein the escalator is usually held at a stop and is started when the presence of a user is detected by a photoelectric device or the like.
The reasons why the escalator is held stopped are to save energy and to extend the escalator's lifetime. In stores etc., however, there is the tendency that when the escalator is held stopped, the number of users thereof decreases to reduce the number of shoppers in the upper floors. Accordingly, a system has been considered wherein in the absence of a user, the escalator is operated at a low speed, while when a user appears, the escalator has its speed switched to a rated speed. Considered for this system is a method which switches the speeds by the use of an A-C two-speed motor, or a method in which the speed of the escalator is controlled by applying a device described in Japanese Utility Model Registration Application Publication No. 58-23824 and varying the primary voltage of a driving induction motor with thyristors or the likes.
The adoption of these methods, however, involves problems.
With the method using the A-C two-speed motor, two sorts of coils for the high speed and the low speed are employed, so that the motor has a large external shape and is difficult to be received in an escalator machinery room of limited space. Another problem is that a great shock develops at the switching of the speeds, so the product lifetime is rather shortened by frequenct switching operations.
On the other hand, although the primary voltage control can mitigate the shock at the switching of the speeds, the efficiency of the low speed mode is very inferior, and the temperature rises abnormally in the motor during ordinary use, so that a motor having a large capacity must be used. Another problem is that the control method is unfavorable from the standpoint of saving energy.